The present invention relates to a turbocharger system.
It is typical for a turbocharged engine to be controlled by an electronic engine management system, using manifold pressure or air mass flow rate as a control variable. With this technology, it would be normal for the turbocharger wastegate to react, such that a desired air mass flow rate or manifold pressure is achieved. The desired rate will depend upon such parameters as engine speed and throttle position.
With a twin-turbocharged engine application, it is typical for a similar control system to be applied. Under normal conditions the turbocharger wastegate positions react in parallel, such that each turbocharger operates with half the total air mass flow rate passing through each.
In the event of a failure, perhaps in the wastegate actuator for example, such that the two turbochargers do not react in parallel, it is necessary for the engine management system to be alerted via self-diagnosis. The engine management system can then activate a fail-safe operating condition (limp-home). If this is not done, the turbocharger carrying the greater air mass flow rate can overspeed, leading to catastrophic failure.
It is not normally possible for the turbocharger speeds to be measured directly.
It is known that it may be possible to diagnose asynchronous turbocharger operation by careful measurement of pressures, either before the turbochorger compressor, or directly after the turbocharger compressor. However, this may be difficult and expensive to achieve. Since it is usual for the two compressor outlets to be connected together before entering a common inlet manifold, the pressures are largely held together, even if the air low rate through one compressor is almost nil. Pressure differentials are small, the detection of which requires high tolerance (expensive) transducers. Under this condition however, the compressor with the higher air flow rate does produce a slightly higher pressure.
According to one aspect of the present invention, there is provided a turbocharger system for use with an internal combustion engine comprising two turbochargers each having a turbine drivably connected to a compressor and temperature sensor means associated with the compressors to enable an imbalance between the two turbochargers to be sensed.
According to another aspect of the present invention, there is provided a method of operating a turbocharger system for an internal combustion engine comprising two turbochargers each having a turbine drivably connected to a compressor including the steps of monitoring the temperature at or adjacent each compressor and comparing the temperature monitored to give an indication of an imbalance condition between the two compressors.
In a preferred embodiment of the invention, the sensor means comprise thermocouples or other temperature sensing elements advantageously disposed at respective outlets of the two compressors. These elements produce electrical signals which enable the temperatures at the compressor outlets to be compared. The signals may be compared in a normal comparator circuit which may or may not form part of the engine management system of the engine to which the turbocharger system is to be fixed. Engine management systems usually incorporate a microprocessor which provides a signal processing function which may be used to process the signal to give an imbalance indication. Where an imbalance condition occurs, the harder working compressor outlet temperature will rise. In addition, because the new compressor operating condition will not be as efficient as the optimum (balanced) compressor condition, there will be a further temperature increase. The temperature difference between the air condition at the two compressor outlets, is sufficient such that it can be measured using inexpensive and reliable thermocouples. In addition, the resolution of imbalance is very much better than that which could be determined by using pressure measurements.